In motor vehicles, the drive axle differential gear system in the power train is an essential component. The primary function of the differential gear system is to translate the engine power through the drive shaft to the wheels for forward and backward propulsion efficiently. At the same time, it must allow one drive wheel to turn faster than the other when the vehicle rounds turns, yet both wheels must receive the proper engine torque.
The traditional design of a differential gear system is characterized by its heavy and rugged construction to absorb the driving force of the wheels. For example, the internal gears of the differential are usually made of high strength hardened steel. Likewise, its casing is made of cast steel. The use of high strength materials provides a large margin of safety in the design and construction of the components. This, coupled with its small number of internal components, makes the differential gear system a relatively reliable piece of equipment in the power train of the motor vehicle. In view of such high reliability, however, maintenance, versatility of mounting and ability to change gear ratio and direction of motion has not always been properly considered and provided for in the design and construction of the system.
A good design should consider not only reliability but also these other aspects of the unit's function and use. As the demand for high performance in motor vehicles increases, new challenges to the traditional designs in equipment and components will also be seen.. For example, the demand for fuel efficiency often dictates the replacement of heavily constructed or rugged components with lighter components or components having different material construction. Likewise, maximizing the power output of the engine often places new stress upon the various parts and components, thereby affecting the overall reliability of the motor vehicle. Other applications, such as racing and off road travel for leisure or military applications, are likely to subject the various parts and components to significant stress factors because of the operating and environmental conditions.
When equipment fails, it must be repaired or restored in a timely manner so as to ensure its availability, i.e., the time that the equipment is operable. When applied to equipment or components, maintainability means the manner in which such equipment or components can be restored to their operable state. As often is the case, a key factor in determining maintainability is the accessibility to the failed or malfunctioned equipment so as to enable the maintenance personnel to diagnose, repair or replace the failed or malfunctioned components.
The traditional differential housing designs do not permit ready accessibility to the gear system or bearings, particularly to change gear ratios or when repairs must be made in the field or in time-critical situations such as racing. In many designs, the housings are made of stamped steel parts welded together. In other designs, the entire housing may be made of cast steel. Accessibility to the interior of most differential gear units is only through a small rear access plate fastened to the housing. However, since all of the bearings and seals are located within the housing itself, any repair or service work to these parts must involve the dismantling of much of the housing and gear system. If the axle is to be repaired or if the gears are to be replaced, the differential housing must be fully disassembled. The traditional design of the differential gear housing thus makes maintenance and repair of the gear system and bearings very difficult.
The accessibility problem is a factor especially serious in a rear engine drive system. In this configuration, the differential gear is usually positioned between the transmission and the engine. Thus, for maintaining or repairing the internal gears or the bearing for the input and output shafts and axles, both the transmission and the engine may have to be dismounted from the chassis of the vehicle before any work can be performed.
Further, for a differential to be truly universal (or "omni") it should be able to be easily re-configured to be able to change the direction of driving motion or to be able to reverse input and output directions.
Accordingly, it would be desirable to have a differential gear housing that is compact, lightweight and easily adaptable to different differential drive configurations. It would also be advantageous to have a differential gear assembly that is easily maintainable. Particularly, it will be highly desirable to have a housing which facilitates repair or replacement of the bearings for the drive shafts and axles without requiring entry of the internal compartment of the differential gear housing. Further, it will be advantageous to have a differential gear housing that is simple to manufacture and easy to install.